Treatment of viscose cellulose filamentary materials



Patented Aug.. 23, 1949 TREATMENT 0F VISCOSE CELLULOSE FILAMENTARY MATERIALS Russell Owens Denyes, Rome,- Ga., assigner, by mesne assignments, to Celanese Corporation of America, a corporation of Delaware Application November 29, 1945, Serial No. 631,729

This invention relates to the purification of freshly formed regenerated cellulose products, especially of those which'have been regenerated from viscose, and has for its object the provision of certain improvements in'the initial stages of the purification treatment. The freshly formed viscosel products contain adherent and occluded acid picked up from the regenerating bath, together with appreciable amounts -of reaction products, -comprising carbon disulde, elemental sulfur, salts and metallic suldes. These require removal in a process generally known as purification. A particularly detrimental impurity is lead sulfide, derived from the lead linings of the coagulating bath conduits. Purification generally comprises a seduence of treatments, such as Washing with warm Water to remove the adherent and occluded acid and water soluble salts, and to distill out the occluded carbon disulfide, treating with a sulfur solvent, such as an aqueous solution of sodium sulfide or of ammonium sulfide, and finally rinsing with lukewarm water. Washing with plain water and desulfurizing with alkaline sulfide solutions do not eectuate complete removal of the metallic suldes. Since these tend to discolor the viscose products, it is the practice of the art to subject the products subsequently to a bleaching treatment as, for example, with chlorine water or with sodium hypochlorite solutions. Such bleaching treatments, however, result in partial degradation of the Vis-cose product due to the unavoidable oxidizingl action on the regenerated cellulose of the bleaching agent employed.

This invention is concerned with the initial washing step in the purification procedure, and has for its object the provision of an improved methodof washing freshly formed viscose products, for example, freshly spun filaments, whereby the normal impurities with the exception of elemental sulfur, are eifectually removed. The conventional subsequent bleaching treatment is rendered unnecessary, and no increase in process time is involved. In accordance with the invention, viscose filaments may be purified while in the gel state in the form of bobbin spinning packages, -pot spun cakes, staple fiber tow, or while passing over the initial thread-storage, thread-advancing devices of continuous spinning machines. l

I have found that viscose filaments in the gel state, while still wet withfadherent acid carried off from the spinning bath, may be purified to a high degree of whiteness without bleaching in the conventional sense, without implicating a 2 significant extension of existing purification schedules and without significant impairment of the tensile characteristics, if the water which is normally employed for washing out the acid is dosed with relatively small amounts of certain chemicals, namely, alkali-metal chlorites, chlorine dioxide or chlorous acid, used singly or preferably, conjointly with a sequesterlng agent, such as sodium hexametaphosphate.

For convenience, the invention will be described with reference to the puriiication of viscose yarn while on the bobbin on which it was spun. It is, of course, understood that the invention is applicable to the purification of viscose filaments in the gel state when produced under other types of spinning. In accordance with the method of the invention, the purication may be carried out by employing a series of separate washes and using a solution containing sodium chlorite at the start of the initial wash of the yarn, for example, during the preliminary acid-removal wash. If the yarn is highly discolored, I may obtain a more satisfactory color removal in a short period of time by the use of a sequestering agent, such as sodium hexametaphosphate, in conjunction with the sodium chlorite. It is sometimes advantageous to employ a short initial acidremoval wash prior to the addition of sodium chlorite when purifying a yarn package that washes slowly. In this way the bulk of the acid is removed from the yarn prior to its exposure to the chlorite ions, and this minimizes the danger of over-exposure and slight damage to the yarn resulting therefrom. When employing an initial wash, the time must be adjusted so that the acidity of the spin package does not drop below the required level prior to completion of the action of the chlorite. This is important since the acidity required for the most effective action of sodium chlorite, in this type of operation, is furnished by the acid remaining in the yarn from the spinning operation.

While the acid may be washed out in the initial wash to any desired extent, it is desirable in certain instances to elect a more certain control over the acidity of the filaments and the treating solution by employing an initial wash of such duration that most of the acid is removed from the spin package. The yarn is then further washed with a precisely acidied solution of sodium chlorite. The initial wash and the second wash may or may not contain a sequestering agent, such as sodium hexametaphosphate, depending upon the nature and degree of the discoloration of the yarn and the extent of bleachot color removal may be accomplished by using a small amount, say 0.1%. of sodium hexametaphosphate in the initiel-acid-removal wash, Such a wash is preferably carried out at a temperature around 60 C. A hot solution is most ellfectlve when using sodium chloritc alone or in conjunction with sodium hexametaphosphate in the initial wash.

The optimum duration and the temperature of the initial wash and of the second wash, concentration of the chlorite or chlorine dioxide. concentration oi the sequestering agent, il' employed, in either or both the initial wash and second wash, and acidity of the yarn or second wash are al1 dependent upon the degree of discoloration of the yarn, the extent o! purification required, and the form of the yarn at the time of treatment, i. e.. type oi yarn package. It is generally desirable to use a temperature in excess or 40 C.. preferably between 50 C. and 60 C. Excellent results on a vhighly discolored yarn have been obtained using concentrations ci sodium chlorite between 0.5 and 1.0 g. per liter. Specific cases may require somewhat higher concentrations, or permit the use oi lower concentrations of this compound. Concentrations of 0.5 to 1.0 g. per liter of sodium hexametaphosphate have proven definitely advantageous in some cases. When an acidiiied purification solution is employed, the preferred acidity of said solution is at least pH 5.5 or more strongly acid.

Sodium chlorite in an acid solution attacks certain metals, even stainless steel, and the resulting corrosion products may impair the color of the yarn. It is advisable to protect the metal from these agents and I have found that bobbins and the like coated with a Bakelite lacquer. such as Heresite. are suitably protected.

In order to make accurate comparisons between viscose filaments treated according to the invention, untreated viscose iilaments and bleached viscose filaments, evaluation measurements were made by means of a General Electric recording spectrophotometer. The results of the invention will, accordingly. be better `understood with reference to the accompanying drawing which is a composite reproduction of the recordings of the spectrophotometer.

The following examples illustrate applications of this invention to purifying viscose yarn on a spin bobbin:

Exsupu: I

A very satisfactory color removal and uniform hiteness was obtained as follows using 150/40 bright viscose yarn:

Purification schedule minutes 0.1% sodium hexametaphosphate (57 0.)-- 100 0.1% sodium hexametaphosphate 0.065% sodium chlorite 0.005% sulfuric acid (57 C) (150 Hot water (57 C.) 200 Ammonium suliide (40 C.) 100 Hot water (57 C.) 100 The yarn package may be characterized as follows:

Same as Example I except that the sodium hexametaphosphate was omitted from the initial hot water wash min.) which-preceded the chlorite treatment. i Exam: III Bobbin purification schedules in minutes on /40 bricht `viscose #am Conventional Treatment o! ooe. Invention 50 HW 100 HW m0 H 150 BS 100 BW 200 HW 100 A l0) A 20 BW 20 HW 80 HW 80 HW HW-hot (50 C.) writer ss :a 50 o.) dlum'enlcn (0.07%). sodium nmmmph hlateul a) sulfuric acid to give pli 4.5-6.5 alter addition ol sodium `Awammonium sulfide (0.35%) at 45 O.

A package produced from the same viscose and spun under identical conditions as in the Conventional Process? yarn was drip-bleached with chlorine water in accordance with the treatment of United States Patent 2,064,300 and used lor whiteness comparison.

Both the yarns of Example DI, the dripbleached yarn, and a well bleached commercial -yarn were cone wound, sampled and a test fabric panying drawing. It is significant to note that the whitest yarns now produced are less white than the cellulose pulp from which the yarn is produced. This indicates the extent of discoloration caused by the viscose process.

I claim:

1. The method of purifying freshly formed viscose cellulose fllamentary materials, which comprises subjectng the materials, while in a gel state and while still containing adherent acid from the coagulating bath, to washing treatments with an aqueous solution containing sodium hexametaphosphate and then with an aqueous solution of sodium hexametaphosphate and a compound selected from the group consisting of alkali-metal chlorites, chlorine dioxide and chlorous acid, the acidity of the latter aqueous solution being at least pH 5.5.

2. The method of purifying freshly formed viscose cellulose filamentary materials, which comprises subjecting the materials, while in a gel state and while still containing adherent acid from the coagulating bath, to washing treatments with an aqueous solution containing sodium hexametaphosphate and then with an aqueous solution of sodium hexametaphosphate and sodium chlorlte, the acidity of the latter aqueous solution being at least pH 5.5. s

A3. The method of purifying freshly formed viscose cellulose iilamentary materials, which comprises subjecting the materials, while in a gel state and while still containing adherent acid from the coagulating bath, to washing treatments at a temperature of 40 to 60 C. with an aqueous solution of sodium hexametaphosphate and then with an aqueous solution containing sodium chlorite and sodium hexametaphosphate, the sodium chlorite and sodium hexametaphosphate being each present in said latter aqueous solution in a concentration of from 0.5 to 1.0 grams per liter, the acidity of the latter aqueous solution being at least pH 5.5, and then subjecting the products to desulfurizing and washing treatments.

RUSSELL OWENS D REFERENCES CITED 5 The following references areof record in the le of this patent:

UNITED STATES PATENTS lNumber Name Date 1,977,533 Thurmond Oct. 16, 1934 2,031,827 Fiske Feb. 25, 1936 2,140,008 Hall Dec. 13, 1938 2,265,033 Fryer Dec. 2, 1941 2,374,100 Jackson Apr. 17, 1945 FOREIGN PATENTS Number Country Date 191,212 Switzerland Aug. 16, 41937 443,498 Great Britain 1935 OTHER REFERENCES Munter et al., Application of Sodium Metaphosphate to Textile Processes, Am. Dyes. Rep. Jan. 28, 1935, pages 40-47. (Copy in 8-82.)

Matthews, Bleaching and Related Processes, 1921, Chem. Cat. Co., N. Y., pages 471-473. (Copy inDiv. 43.) 

